They really need to fix the mod building thumbnails not showing up in the game. Looking for a specific modded building is such a pain in the ass once you accumulate a bunch of them.
The thing is, some mod authors have gotten them to work, but I'm not sure how they're doing it. I only use custom made assets that have preview icons now, because like you said, it's a huge pain in the ass to hover over each and every mystery icon to find the building you're looking for.
I remember the patched the game during the pre-release week when all the streamers were playing it, and they patched it a week and a half after that, so here's hoping they'll keep pushing out patches every couple of weeks. Really excited about tunnels, hope we get a better idea of when that functionality is going to make it into the game soon.